AS OBSER'^^ED IN TORRICELLIAN AND OTHER VACUA. 
155 
have often observed beyond the clear cloud-like stratifications towards the negative, seve- 
ral faint but clearly-defined striae or bands ; when repeating Mr. Grove’s experiment, of 
allowing the discharge to be intercepted between two metallic points attached to the 
coil*, I observed that however short might be the interval by which the discharge was thus 
separated, these faintly illuminated striae or bands always vanished, leaving the clear 
clouds without change of form ; for this experiment I use my micrometer-electrometer, 
described by me in the Philosophical Transactions, Part I., 1840, and in which, by 
means of the micrometer screw, I can obtain a separation of swotk of inch. 
103. Most striking and beautiful efiects of the stratified discharge were obtained in 
a large glass cylinder, of about 4-|^ inches internal diameter, in which brass wires 
were hermetically sealed about 20 inches apart. The caustic potash being inserted in 
the narrow portion, the cylinder was charged with carbonic acid gas, and exhausted in 
the usual manner. With one wire attached to the outer positive terminal of the coil, the 
stratifications (large cloud-like form) are very clearly defined and most remarkably sensi- 
tive to inductive action, by the approach of the hand ; on the four fingers being success- 
ively placed on the stratifications, the stratifications disappear in succession ; but while in 
this state, if a powerful electro-magnet is put in action close to the negative, the stratifi- 
cations reappear and pass by the fingers of the hand, which during the experiment rest on 
the glass ; the power of the magnet overcoming the inductive resistance. The stratifica- 
tions in this apparatus can be separated for a considerable space by placing both hands 
on two separate portions of the cylinder ; and if one hand is placed within about 2 inches 
of the positive wire, where two or three clouds are then visible, and the other hand is 
placed on the cylinder about 4 to 6 inches nearer the negative, a large single cloud will 
be brought out in a very striking manner, showing that even where stratifications are no 
longer -visible, they can be elicited by the mere effect of induction. If the wire pre- 
\iously attached to the outer is connected -with the inner terminal of the coil, the efiects 
of induction, by the approach or even on touching the cylinder, cannot be obtained, but 
the pov/er of the magnet to draw out a further number of the stratifications is equally 
strong as before. 
General Conclusions. 
104. From the absorption of carbonic acid by caustic potash, we not only obtain a far 
more perfect vacuum than the Torricellian, but the process of absorption is so gradual, 
that we are enabled to examine with much accuracy the different phases which the 
electrical discharge assumes. With the air-pump vacuum, a discharge that will not 
pass one inch in air will, in the form of a wave-discharge, pass from -wire to wire through 
30 or 40 inches, or even more ; and as the vacuum improves by the absorption of the 
carbonic acid, the discharge gradually fills the tube with a luminous glow, showing 
narrow stratifications commencing at the positive -wire, the negative wire being sur- 
rounded with a blue glow ; as the vacuum continues to improve, the narrow stratifica- 
tions extend throughout the discharge to about one inch of the negative wire, where 
* See note at end of this paper. 
T 2 
